1. Field of the Invention
The present invention relates to a method and apparatus for measuring an altitude. More particularly, the present invention relates to a method and apparatus for measuring an altitude of a portable terminal capable of improving accuracy at the time of measuring the altitude using a barometer.
2. Description of the Related Art
Along with the development of information communication technologies and semiconductor technologies, distribution and use of a portable terminal is on the rapid increase. The portable terminal provides various functions such as a calling function, a music replay function, a text message transmission and reception function, a digital broadcast reception function, a near field communication function, and an Internet connection function. Particularly, portable terminals having a function of measuring an altitude are increasing.
Some examples of methods of measuring the altitude are a method of using a property that atmospheric pressure changes as the altitude increases on the basis of the sea level, a method of triggering an electronic pulse from an airplane to a ground and calculating an altitude by measuring round-trip time of the triggered electronic pulse between the airplane and the ground, and a method of measuring an altitude of the current location by calculating a distance to the satellite by a difference between a reference time and a signal transmission time by receiving the signal triggered from a Global Positioning System (GPS) artificial satellite. However, the method of using the electronic pulse and the method of using GPS generally uses an expensive device that cannot be easily accessible. Further, the method of using the GPS has an error ranging from several meters up to tens of meters and thus is not reliable, and cannot receive the GPS signals inside a building. Hence, the portable terminal generally uses a method of measuring an altitude using an atmospheric pressure change according to the increase of the altitude.
The method of measuring the altitude using the atmospheric pressure change uses a principle that the atmospheric pressure gradually decreases as the altitude increases, and the altitude may be calculated using the measured atmospheric pressure and the reference atmospheric pressure (e.g., the sea level atmospheric pressure) by Equation 1 below.z=cT log(p0/p)  Equation 1
Here, “z” denotes the current altitude, “P0” denotes the reference atmospheric pressure (e.g., the sea level atmospheric pressure), “p” denotes the current atmospheric pressure, “c” denotes a constant, and “T” denotes the absolute temperature. For example, the portable terminal may calculate the current altitude based on the reference atmospheric pressure (e.g., sea level atmospheric pressure) and the current atmospheric pressure, under the assumption that the current temperature is a room temperature (e.g., 25° C.).
To this end, the related-art portable terminal stores the reference atmospheric pressure (e.g., sea level atmospheric pressure) in advance or permits a user to input the reference atmospheric pressure at the current location at the time of measurement. However, in the case in which the reference atmospheric pressure was registered in advance, the reference atmospheric pressure is changed according to the weather condition and temperature, etc., and thus the accurate altitude cannot be measured. In other words, the related-art method of measuring the altitude may have errors in the calculated altitude if the reference atmospheric pressure is not frequently updated because the reference atmospheric pressure is momentarily changed along with the change of time or weather.
Further, according to the related-art method of measuring the altitude, if the reference atmospheric pressure is input from the user, the user should always recognize the reference atmospheric pressure at the current location or should determine the reference atmospheric pressure from a website that provides the reference atmospheric pressure such as a weather center, etc. In particular, according to the related-art method of measuring the altitude, if the user does not know the reference atmospheric pressure at the current location, the altitude cannot be measured. Further, the reference atmospheric pressure provided by the weather center is the reference atmospheric pressure measured in a weather station closest to the current location. Hence, even if the reference atmospheric pressure is received through the weather center, the current altitude calculated by the above Equation 1 may have an error. For example, according to the related-art method of measuring the altitude of the portable terminal, the reference atmospheric pressure is changed according to the change of time and weather, and thus it is difficult to calculate the accurate altitude, and if the altitude is intended to be corrected by correcting the reference atmospheric pressure, it is inconvenient for the user to obtain and re-input the accurate reference atmospheric pressure.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.